A combustion section of a gas turbine generally includes a plurality of combustors that are arranged in an annular array around an outer casing such as a compressor discharge casing. Pressurized air flows from a compressor to the compressor discharge casing and is routed to each combustor. Fuel from a fuel nozzle is mixed with the pressurized air in each combustor to form a combustible mixture within a primary combustion zone of the combustor. The combustible mixture is burned to produce hot combustion gases having a high pressure and high velocity. The combustion gases are routed through the combustor and into a turbine of the gas turbine. Thermal and kinetic energy are transferred from the combustion gases to various stages of rotatable blades coupled to a rotor shaft, thereby causing the rotor shaft to rotate. The rotating shaft produces mechanical work. For example, the rotor shaft may be coupled to a generator to produce electricity.
Various factors influence the design and operation of the combustors. For example, higher combustion gas temperatures generally improve the thermodynamic efficiency of the combustors. However, higher combustion gas temperatures generally increase the disassociation rate of diatomic nitrogen, thus increasing the production of nitrogen oxides (NOX). In addition, gas turbine operators may prefer to use different types of fuels depending upon availability and price. However, various fuels such as liquefied natural gas and heavy fuel oil may have a high level of fuel bound nitrogen, thereby resulting in high levels of NOx emissions when the combustion gases are above certain combustion temperatures. As a result, such fuels generally require the use of selective catalytic reduction (SCR) and/or other processes in order to reduce the level of NOx emissions. However, the use of SCR and/or other processes required to reduce the undesirable NOx levels add to the overall operating costs and the overall complexity of the gas turbine engine.
Another approach to reduce NOx production from fuel bound nitrogen is a combustor having a rich-burn combustion zone, a quick-mix or quick-quench zone that is downstream from the rich-burn combustion zone, and a lean-burn combustion zone that is downstream from the quick-quench zone. This combustion technology is commonly known as a Rich-Burn, Quick-Quench and Lean-Burn (RQL) combustion system. The RQL combustor may be used in conjunction with the SCR. In large part, the effectiveness of the RQL combustor is primarily dependent on the design of the venturi of the quick-quench zone of the RQL combustor. Therefore, an improved RQL combustor, in particular an improved quick-quench zone for an RQL combustor would be useful in the industry.